Advance Journal of Food Science and Technology 8(11): 785-791, 2015

Advance Journal of Food Science and Technology 8(11): 785-791, 2015
ISSN: 2042-4868; e-ISSN: 2042-4876
© Maxwell Scientific Organization, 2015
Submitted: December 10, 2014
Accepted: January 27, 2015
Published: July 15, 2015
Role of Konjac Flour on Emulsifying Property of Milk and Egg White Proteins and
Sensory Acceptance of Gluten-free Cakes
Adisak Akesowan
Department of Food Science and Technology, School of Science and Technology, University of the Thai
Chamber of Commerce, 126/1 Vibhavadee-Rangsit Road, Dindaeng, Bangkok 10400, Thailand,
Tel.: 662-6976521; Fax: 662-277-7007
Abstract: This study was aimed to investigate the effects of three independent variables: Konjac concentration (0.10.4%), pH level (pH 5-9) and NaCl concentration (0.2-0.6 M) on Emulsifying Activity (EA) of Milk Protein
Concentrate (MPC) and Egg White Powder (EWP). Response surface methodology was used to determine the
effects and also find out the optimal condition. Both Konjac concentration and pH level had greatly significant
effects on EA of MPC and EWP, while NaCl concentration had negligible. An increase in Konjac concentration
showed a positive effect to increase the EA of both MPC and EWP. Moreover, their EA values were found to be
more pronounced at pH 6.5-7.5. The interaction of Konjac concentration and pH level had a negative effect on EA.
The optimal conditions improving the EA of MPC and EWP were applied to the processing of gluten-free rice
cakes. Sensory acceptance of gluten-free cakes added with Konjac flour was evaluated using a 9-point hedonic scale
test. Incorporation of 0.25% Konjac flour was appeared to increase sensory scores of the gluten-free cake and
showed no significant difference compared to the cake containing 0.4% Konjac. Panelists preferred the gluten-free
cakes containing Konjac and were willing to purchase the products.
Keywords: Emulsifying properties, gluten-free cake, Konjac flour, milk and egg white proteins, response surface
Konjac flour is a water soluble, non-ionic high
polysaccharide containing about 70-85% glucomannan.
The flour is extracted from tubers of Amorphophallus
konjac. Its chemical structure is found to be a linear
chain of β-1, 4-linked D-mannose and D-glucose in the
ratio of 1.6:1 with a low degree of acetyl groups (Yang
et al., 2006). Due to its β-linkage structure in which
human enzymes do not hydrolyze, the Konjac is of
interested appreciation as a non-caloric gum for
applying in low-calorie food products. Konjac flour is
one of the most viscous dietary fibers which has been
commonly used to thicken the viscosity of the food
system (Chua et al., 2010). This flour was approved to
use as an additive for gelling, thickening, texturizing
and binding in various food products (Zhang et al.,
2005; Akesowan, 2010). Apart from the technological
effect, the Konjac is also associated with health benefits
in terms of controlling weight gained and obesity,
improving intestinal activity such as bowel movement
and alleviated constipation as well as lowering of blood
cholesterol and triglycerides (Takigami, 2000). As a
consequence, the application of Konjac seems to
simultaneously obtain both technological and health
promoting effects in the finished products.
Celiac disease, which approximately found one in
hundred people, is considered as an important public
health issue (Shevakani and Singh, 2014). At the same
time, most celiac persons play more attention on
In the recent years, an upward trend for
hydrocolloid or gum utilization in multi-component
food system consisting of polysaccharides, proteins and
fat has been observed. Gums have been extensively
used in food products for many purposes such as
gelling and thickening effects, foaming stabilization,
emulsion modification and syneresis reduction during a
freeze-thaw cycle (Rosell et al., 2007; Kovácová et al.,
2009). In addition, they have been successfully used to
retard staling behavior in bakery products, improve the
eating quality of pastas and noodles and extend frozen
dough and bread storage (Asghar et al., 2007). As seen
in the work of Preichardt et al. (2011), a neutral, nongelling polysaccharide named ‘galactomannan’ can be
applied to improve rheological properties of heatinduced whey protein gels. Another study was found
with the achievement of carrageenan addition
incorporated with adjusting protein solution to pH 6.0
in the presence of 0.2 M NaCl for improving
emulsifying properties of milk protein concentrate or
sodium caseinate (Mena-Casanova and Totosaus,
2011). The complex formation developed by specific
protein-hydrocolloid interactions was responsible for
substantially improving emulsifying characteristics,
foaming and rheological properties (Mishra et al., 2001;
Herceg et al., 2007).
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
alternatives they should consume (Demirkesen et al.,
2013). Thus, many research studies in gluten-free
products have continued to increase. At now, the food
product which is healthy, tasty and free of gluten would
be a better choice for celiac patients to decrease adverse
effects of gluten allergy. Generally, celiac disease
causes digestive problems (pain and discomfort in the
digestive tract, gas, chronic constipation and diarrhea),
inflammation of intestinal cells subjecting to reduce
ability to properly absorb nutrients from food, iron
deficiency anemia, vitamins and minerals deficiencies
as well as a severe skin rash called dermatitis herpetic
form is and seizure (Sammu et al., 2010). Rice flour, a
non-gluten ingredient, is used as a wheat flour
alternative for making cakes, cookies and breads.
However, it has not similar functional properties as
wheat flour; due to it has lower protein and no gluten
which contributes to gas retention in batter/dough and
protein network formation during baking (Gallagner
et al., 2004). Unavoidably, it is appeared that
diminished viscoelastic properties of dough and lower
quality of non-gluten rice products were observed in
non-gluten rice products (Maghaydah et al., 2013).
Various hydrocolloids such as xanthan gum, guar gum
and carboxy methyl cellulose have been used to thicken
the viscosity of gluten-free batter/dough. A higher
batter viscosity, a more tiny air bubbles entrapped in the
batter, which expand during baking, thus improving the
quality of rice-based bakery products (Sammu et al.,
2010; Preichardt et al., 2011; Ranjbar et al., 2012). In
addition, a longer shelf life and lower staling behavior
were found in the gluten-free muffins and cakes
incorporated with xanthan gum (Preichardt et al.,
2011). To date, the use of Konjac flour in the glutenfree rice cake has not yet been investigated.
Response Surface Methodology (RSM) has been
extensively used to explore the effects of independent
variables on the responses and also to optimize the best
condition for the process variables (Anderson and
Whitcomb, 2005). At present, there is limited
information involving the use of the RSM to study the
properties of milk and egg white proteins added with
Konjac flour. Therefore, this work aimed to understand
the influence of various levels of Konjac, pH and NaCl
on emulsifying property of Milk Protein Concentrate
(MPC) and Egg White Powder (EWP) using RSM. The
optimal conditions to obtain the maximized values of
the properties were investigated. Also, sensory
evaluation of gluten-free rice cakes incorporated with
optimal levels of Konjac flour was studied.
used. Refined corn oil and cake ingredients included
wheat and cake flour, sugar, salt, fresh eggs, soybean
oil, evaporated milk and baking powder were purchased
from a local supermarket.
Emulsifying activity: The emulsion capacity was
determined according to the method of Yasumatsu et al.
(1992) with some modification. To prepare emulsion,
25 mL of corn oil and 25 mL of protein solution with
different levels of variables were mixing by a blender at
speed 2 for 1 min. After centrifuging at 2000×g for 15
min, the mixture was poured into a 100-mL cylinder
and then the height of emulsified layer was measured.
All analyses were performed in 7 replications.
Emulsifying Activity (EA) was expressed as a
percentage of the height of emulsified layer in relation
to total liquid content.
Experimental design: The protein was employed at
1% (w/v). Five levels (-1.68, -1, 0, 1 and 1.68,
respectively) containing twenty experimental treatments
were run using a Central Composite Rotatable Design
(CCRD) with 3 independent variables including
Konjac, pH and NaCl. The coded and actual values
used for this experimental design are shown in Table 1.
The predictive models for EA of MPC and EWP are
proposed in the equation below:
Y = b0 + b1X1 + b2X2 + b3X3 + b11X12 + b22
X22 + b33X32 + b12X1X2 + b13X1X3 + b23X2X3
where, Y is the predictive response; X1, X2 and X3 are
independent variables such as Konjac concentration
(%), pH level and NaCl concentration (M); b0 is the
intercept and b1, b2 and b3 are linear, b11, b22 and b33 are
quadratic and b12, b13 and b23 are interaction coefficient,
Cake preparation: The standard cake was prepared
based on flour weight basis. Initially, 100 g wheat flour,
112.4 g sugar, 3 g salt and 3 g baking powder were
thoroughly mixed in a bowl by hand. The 55.5 g egg
yolk, 30 g soybean oil, 30 g water, 120 g orange juice
and 3 g vanilla flavor were well mixed in another bowl.
The liquid mixes were poured into the dry ingredients
bowl and then well mixed with an eggbeater until
smooth (about 2 min). The whipped egg white was
prepared by whipping 100 g egg white, 0.7 g salt and
0.5 g cream of tartar until the soft peak was formed.
The 24 g sugar was added and whipped to form firm,
moist peaks. The whipped egg white was folded into
the flour-liquid mixture, gently mixed and immediately
deposited into cake pans. The batter was baked at 170180°C for 25-30 min. The cake was allowed to cool for
1 h, packed in low density polyethylene bags and kept
at room temperature (29-30°C) for the next day
Materials: Konjac flour (Chengdu Newstar Chengming
Bio-Tech Co., Ltd., Chengdu, Sichuan, China), milk
protein concentrate (MPC 80, Vitalus Nutrition, Inc.,
Abbotsford, Canada) and egg white powder (egg
albumen) (Michael Foods, Inc., Minnesota, USA) were
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
Table 1: Three dependent variables with coded and actual values and results of EA of MPC and EWP
concentration, pH level and NaCl concentration
Coded (actual) values
-----------------------------------------------------------------------------------------------------Experimental run
Konjac concentration (%)
pH level
NaCl concentration (M)
-1 (0.10)
-1 (5)
-1 (0.2)
+1 (0.40)
-1 (5)
-1 (0.2)
-1 (0.10)
+1 (9)
-1 (0.2)
+1 (0.40)
+1 (9)
-1 (0.2)
-1 (0.10)
-1 (5)
+1 (0.6)
+1 (0.40)
-1 (5)
+1 (0.6)
-1 (0.10)
+1 (9)
+1 (0.6)
+1 (0.40)
+1 (9)
+1 (0.6)
-1.68 (0.00)
0 (7)
0 (0.4)
+1.68 (0.50)
0 (7)
0 (0.4)
0 (0.25)
-1.68 (3.6)
0 (0.4)
0 (0.25)
+1.68 (10.4)
0 (0.4)
0 (0.25)
0 (7)
-1.68 (0.06)
0 (0.25)
0 (7)
+1.68 (0.74)
0 (0.25)
0 (7)
0 (0.4)
0 (0.25)
0 (7)
0 (0.4)
0 (0.25)
0 (7)
0 (0.4)
0 (0.25)
0 (7)
0 (0.4)
0 (0.25)
0 (7)
0 (0.4)
0 (0.25)
0 (7)
0 (0.4)
MPC: Milk protein concentrate; EWP: Egg white powder; EA: Emulsifying activity (%)
analysis. The gluten-free cakes were made by replacing
wheat flour with rice flour in the absence and presence
of Konjac flour at optimal levels.
under various levels of Konjac
EA (%)
Table 1. The EA of MPC ranged from 31.9 to 98.2%,
while that of EWP ranged from 21.4 to 93.9%,
respectively. The statistical analysis for regression
coefficients, sum of squares and p-values of responses
of MPC and EWP is shown in Table 2. There were
linear, quadratic and interaction effects on each model.
The EA model of MPC was significant and its
determination coefficients (R2) was found to be 0.9793,
while that of EWP was also effective with R2 of 0.9951.
The results indicated that the fitted model accounted for
more than 97% of the variance in the experimental data.
Moreover, their high R2 values confirmed the good
correlation between the experimental and predicted
values (Koocheki et al., 2010). Here, both models also
displayed no significant (p>0.05) lack of fit values
(Table 2), consequently advocating the reliability and
accuracy of the EA models of MPC and EWP. The
fitted EA models with significant actual factors were
described in the following Eq. (2) to (3):
Sensory evaluation: Initially, the sensory acceptance
of wheat and gluten-free rice cakes containing 0, 0.25
and 0.4%, respectively Konjac flour was evaluated
using 9-point hedonic scale test (1 = extremely dislike,
9 = extremely like). Panelists were invited to assess
theses sensory attributes including appearance, taste,
texture and overall acceptability. In addition, a 5-point
scale test (1 = certainly would not buy, 5 = certainly
would buy) was used to assess for product purchase. All
sensory tests were conducted by 100 untrained panelists
from the University of the Thai Chamber of Commerce,
Thailand. Panelists were invited to rinse their palates
before testing each sample.
Statistical analysis: All experiments were carried out
in triplicate. Data were analyzed for regression and
Analysis of Variance (ANOVA) using the DesignExpert Trial Educational version 8.0.2 software (StateEase Inc., Minneapolis, Minnesota, USA). For glutenfree cake study, sensory data were conducted on a
Randomized Complete Block Design (RCBD). Means
with a significant difference (p<0.05) were compared
using Duncan’s new multiple range test (Cochran and
Cox, 1992).
MPC = -149.19 + 349.49X1 + 60.98X2 - 14.08X1X2
- 369.13X12 - 4.60X22
EWP = -33.94 + 349.73X1 + 33.45X2 - 8.46X1X2
+ 7.41X2X3 - 552.82X12 - 3.12X22
Analysis of response surface plots: From Table 2, EA
of both MPC and EWP were significantly affected by
linear and quadratic terms of Konjac concentration and
pH level at p<0.001, while NaCl concentration was not
found to be significant at p<0.05. The interaction of
“Konjac concentration and NaCl concentration” was
found to be significant at p<0.05 and p<0.01 on EA of
MPC and EWP, respectively. In addition, the EA of
Statistical analysis and model fitting: Results of
different levels of Konjac concentration, pH and NaCl
concentration on emulsifying activities of MPC and
EWP determined by a CCRD design are presented in
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
Table 2: Coefficients of responses, sum of squares and p-values of EA of MPC and EWP
X1: Konjac concentration
X2: pH level
X3: NaCl concentration
Lack of fit
*: Significant at the 99.9% level if p<0.001, 99% level if p<0.01 and 95% if p<0.05; Coef.: Correlation regression; S.S.: Sum of squares; EA:
Emulsifying activity (%); X1: Konjac concentration (%, w/v); X2: pH level; X3: NaCl concentration (M)
emulsion. Nevertheless, the interaction of “Konjac
concentration and pH level” had a negative effect
(Table 2), which caused a rapid decrease in EA of MPC
and EWP when 0.4% Konjac concentration and pH at 9
were applied.
Figure 1b and e show that, at pH 7, the variation of
NaCl concentration (0.2-0.6 M) did not affected EA of
MPC and EWP. Increasing of Konjac concentration
promoted the increment of EA of the proteins,
indicating that the Konjac would be potential to interact
with MPC and EWP to generate the proteins-Konjac
complexes with strong interactions as the pH system
was at pH 7. This finding was not consistent with the
work of Mena-Casanova and Totosaus (2011) who
presented that both higher pH values (pH>6) and ionic
strength (NaCl>0.2 M) were parameters to decrease the
emulsifying capacity of the protein-carrageenan
mixtures. It was probably due to the Konjac is a nonionic polysaccharide, not as anionic polysaccharides
like kappa carrageenan, where sodium salts affect the
sulfated ester groups and inhibit the helix formation of
kappa carrageenan (Nussinovitch, 1997).
The effects of pH level and NaCl concentration on
EA of MPC and EWP, where the Konjac concentration
was at 0.4%, are presented in Fig. 1c and f. An increase
in NaCl concentration had no effect on EA, while the
EA of the both proteins tended to decrease at a high pH
level (pH 8-9). The reduction of electrostatic
interactions between polysaccharides and protein
micelles considered to be a factor causing the instability
of emulsion (Spagnuolo et al., 2005). It was also found
that the interaction of “pH level and NaCl
concentration” had a negative effect on the EA of EWP
(Fig. 1f), showing a rapid decrease in EA at higher
levels of pH (pH 8-9) and NaCl concentration (0.5-0.6
EWP was significantly affected (p<0.01) by the
interaction of “pH level and NaCl concentration”. The
effect of Konjac concentration, pH level and NaCl
concentration on EA of MPC is given in Fig. 1a to c
and that of EWP is in Fig. 1d to f. Response surface
graphs were plotted between the independent variables
while keeping another independent variable at the zero
coded level. It was seen that the graphs of both MPC
and EWP demonstrated similar manners. In this study,
the maximum amount of oil dispersing in an aqueous
solution was measured and defined as EA. The EA is
the result of soluble and insoluble protein fractions and
other components such as polysaccharides. Regarding
the results in Fig. 1a and d, at 0.4 M NaCl
concentration, it was observed that both MPC and EWP
exhibited the most EA at the optimal pH ranged from
6.5 to 7.5 and their EA values tended to decrease as the
pH was either lower or higher than the optimal pH
level. An increase in Konjac concentration from 0.1 to
0.4% increased the emulsified layer phase or EA of
MPC and EWP. This indicated that the Konjac flour has
an ability to enhance EA of the both proteins, which
was attributed to it can increase the viscosity of
continuous aqueous phase to prevent or retard oil
droplets come to flocculate or coalesce, consequently
the droplets still disperse individually in the aqueous
medium contributing to the good emulsion system
(Alleoni, 2006). This was confirmed by the study of
Mena-Casanova and Totosaus (2011), which improved
emulsifying properties of milk proteins with kappa and
lambda carrageenans. They revealed the increase of
emulsifying properties as a result of functional
properties of the carrageenans to greater the oil
incorporated into the emulsion before breaking down.
Farshchi et al. (2013) stated that the interaction
between protein-polysaccharide (milk protein-locust
bean gum) molecules promoted strengthen and thicker
interfacial layer, which was associated with the steric
repulsion on oil droplets and protected the droplets
against the flocculation sand coalescence. This can
stabilize and enhance kinetic stability of the oil-water
Optimization and validation: The optimal levels of
Konjac concentration, pH level and NaCl concentration
to achieve the best emulsifying properties of
MPC and EWP were determined using the Design788
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
Fig. 1: Response surface graphs for EA of MPC (a-c) and EWP (d-f) under various levels of Konjac concentration, pH level and
NaCl concentration
Table 3: Sensory scores of gluten-free rice cakes with Konjac flour
Sensory scores**
Overall acceptability
Means in the same column with different superscripts are different (p<0.05); *: Formulation included: C: Wheat cake; T1: Gluten-free rice cake;
T2: Gluten-free rice cake containing 0.25% Konjac flour; T3: Gluten-free rice cake containing 0.4% Konjac flour; **: Based on a 9-point hedonic
scale test (1 = extremely dislike, 9 = extremely like)
Expertsoftware. The optimized condition obtaining the
maximized EA (98.2%) for MPC was found to be 0.4%
Konjac concentration, pH 6.81 and 0.23 M NaCl
concentration, which had a desirability value of 0.961.
For EWP (EA = 97.6%), the condition with 0.25%
Konjac concentration, pH 7.12 and 0.3M NaCl
concentration was found to be optimal (desirability
value = 0.997).
The suitability of the models was carried out using
the recommended optimal conditions. The experimental
results (n = 3) of EA determined in MPC and EWP
were 97.5 and 96.2%, respectively, which were close to
the predicted values, indicating that the models are
quite accurate in prediction.
product decreased in appreciated characteristics. It is
possibly because the difference in functional properties
between wheat and rice flour. Wheat flour contains
gluten which is predominant for water holding capacity;
consequently, it promotes a viscous batter that
potentially entraps air bubbles occurred during a mixing
process. When baking, the high temperature causes
these bubbles to expand the stretchy gluten from the
flour, resulting in a risen batter, loss of gluten elasticity
and final formation of permanent cake structure. This
specific property cannot found in the rice flour
(Preichardt et al., 2011). The addition of 0.25% Konjac
flour significantly increased (p<0.05) all sensory
attributes of the T2 cake, in exception of taste with
respect to the T1 cake. The T2 cake had better product
characteristics, namely higher in volume and height,
small air cells dispersion in crumb and softer texture,
leading to increase in consumers’ palatability. Again in
Table 3, the overall acceptability score of the T2 cake
was found to be 7.3, indicating as well accepted in a
level of moderate preference, which was influenced by
increasing texture quality as a result of 0.25% Konjac
addition. Although the use of 0.4% Konjac tended to
Sensory evaluation of gluten-free rice cakes added
with Konjac flour: Table 3 presents the results of
sensory evaluation of gluten-free rice cakes added with
Konjac flour. It can be seen that the gluten-free cake
(T1) had significantly lower (p<0.05) scores for all
sensory attributes, in the exception of taste as compared
with the wheat Cake (C). This indicated that the total
wheat replacement with rice flour alone caused the
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
Frequency distribution (%)
Konjac flour had significantly higher (p<0.05) scores
for appearance, texture and overall acceptability
compared to the no added Konjac, gluten-free cake. The
panelists were more likely to purchase the wheat cake
equal to gluten-free cakes with 0.25 and 0.4% Konjac
The author is thankful to the University of the Thai
Chamber of Commerce, Thailand, for financial support.
Purchasing score
Fig. 2: Frequency distribution of purchasing decision of
gluten-free rice cakes with Konjac
Flour: C = control wheat cake and T1 to T3 are glutenfree rice cakes with 0, 0.25 and 0.4% Konjac flour,
respectively; Based on a 5-point structured scale test
(1 = certainly would not buy, 5 = certainly would buy)
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effectively and greatly aid in cake characteristics, there
was no significant sensory differences (p>0.05)
compared to the cake with 0.25% Konjac. Thus, the use
of 0.25% Konjac flour seems to be sufficient for
improving characteristics and sensory acceptance of the
gluten-free cake.
The results of consumer purchase of gluten-free
cakes, with and without Konjac, compared to the wheat
cake are given in Fig. 2. The frequency distribution of
purchasing decision at score of 5 and 4 (would certainly
or possibly buy the product) found in the wheat control,
T1, T2 and T3 cakes were approximately 68, 10, 72 and
72%, respectively. At the same time, the T1 cake was
mostly chosen at score of 2 and 1 (would certainly or
possibly not buy the product), revealing that 64%
panelists were unlikely to the product characteristics.
They also comment that the T1 cake (no added Konjac)
had more dense and compact crumb texture. This
finding was in agreement with the acceptance test in
Table 3, showing that significantly lower scores of
appearance, texture and overall acceptability were
found in the T1 cake.
The RSM was effective to describe how Konjac
concentration, pH level and NaCl concentration
influencing on EA of MPC and EWP. The higher EA
was more evident by increasing Konjac concentration,
especially at the pH of 6.5-7.5. At the lowest Konjac
concentration (0.1%) and pH 9, the EA of MPC and
EWP was found to be the lowest. The NaCl
concentration had a slight effect on EA. The maximum
EA of MPC was achieved by using 0.4% Konjac
concentration, pH 6.81 and 0.23 M NaCl concentration,
whereas the condition of 0.25% Konjac concentration,
pH 7.12 and 0.3 M NaCl concentration was optimal for
EWP. The gluten-free rice cake containing 0.25%
Adv. J. Food Sci. Technol., 8(11): 785-791, 2015
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